nasty noise TD30 kvpro

[markfireprime]

Hey guys could use a little help please Im getting nasty noise from my td30 (vexed) its turning up as a low hum though mian outs and though the direct outs NOT though the head phones.. its really giving the the #$%$'s as i gig live with the kit and ive know its been there a while but at low level gigs i can hide but on the week end I had a gig with a metal band and the extra volume made the noise really stand out..... any ideas please?

[mkok]

Are you running it through a DI box so you can do a ground lift?

[MS-SPO]

Hi,

sounds like you successfully built an unintended ground loop. A typical loop would be a) TD-30 main cable shielding to b) amplifier to c) its power supplies ground connection to d) power supply from TD-30 to e) main cable shielding. I assume you plug-in a headphone into the phone connector, so this one can't close the loop.

A quick fix could be just to unplug a power connector, turn it by 180 degree and replug it - if the power plug allows it.

A way to localize is to unplug cable by cable, until the hum disappears. You may need several combinations of unplugging. Candidates are all power supply cables, all analog signal lines, all USB lines etc. - whatever cable you attach anywhere in the whole setup. With some bad luck you need a special power line insulator, which breaks the loop by some electronic circuitry (i.e.some transformer connected correctly).

You can also try to reduce the area encircled by that loop, but usually yoiu have a lot of compensating connected areas, so the effect would be hardly audible. (Remember, loops are inductors, which are sensitive to variable magnetic fields, and are most effective with large areas and many windings.)

Best, Michael

P.S.: you mention, the hum level varies from gig to gig. I assume you have to unplug everything after a gig and replug somewhere else for the next gig? If so, this is another hint, as you will hardly ever recreate the same geometrical loop configuration from gig to gig. In consequence, the hum will sometimes be loud and sometimes be soft ...

[MS-SPO]

The first image on this page ( http://www.angelfire.com/electronic/...und_Loops.html ) nicely demonstrates the problem.

Electrical loops are everywhere. Some hurt, some don't.

Best, Michael

[markfireprime]

OK that looks like a nasty issue. does appear the more lines used the more noise eg master out left only= only a little noise ( pain in the butt at high volume) but with each extra direct out it gets worse. I normally have and 8 channnel 1.5 meter snake for the direct outs and separate leads for the master. these got right into the multi core. with power running here and there for powered side fill lights the td30 ect ect i really dont know how im going to get all this sorted .. will being trying a power conditioner this week but from what you guys are saying its not going to help Btw all those that talk about onstage sound.. you cant beat an old mackie 15 inch powered speaker as side fill.. cheap as chips 2nd had now. almost bullet prof.. dam heavy

[MS-SPO]

Yeah, that's the moment to have a closer look at your gear and how everything is connected. Before adding more stuff, which can make things even worse, carefully check your power connections. A good thing to do is a star-like connection, which means: you feed all, at least many, devices from one point with power, rather then plugging the supplies wherever you get a hold of (encirceling huge areas). But the first thing to do ist to find the dominant one or two loops in your setup. Else it's a bit like driving at high speed in fog ...

The drawing on this page illustrates this approach: http://smud.apogee.net/comsuite/cont...ilid=s&id=1574

Have an eye on other cables, which may destroy the star and create a loop again, like routing something from (2) to (3) and from (3) to (4) in the diagram ...

[MS-SPO]

Once you know the sensitve loop(s) here is a common alternative: user ferrit cores. This increases the electrical impedance for the humming signal propagating along the outer shieldings.

A common means is using a closed (closed !) ring core, like this http://cdn.pollin.de/article/big/G250170.JPG , where you wind the power- or signal cable a couple of times, similar to this http://www.cti-modellbau.de/images/p...s/ringkern.jpg . (In this image both core and cables are much smaller than what you need, and your cable is a compound ... but you'll get the idea ;-) The closed core keeps the magnetic field lines inside the ferrit, running in circles forever, loosing energy.)

A probably less effective way is using plug-on ferrites, as we know form computer cables, like this one: http://cdn.pollin.de/article/big/G250268.JPG .

For the ring cores make sure you stay with the looping direction of the cables around the core. E.g. a "clever" bypass, which let the current encircle 2 times right and 2 times left is netto zero times looping, i.e. giving not the faintest effect ... Just in case there's the argument "I can't fiddle my cable through" - use the plug-on cores instead.

[MS-SPO]

OK that looks like a nasty issue. does appear the more lines used the more noise eg master out left only= only a little noise ( pain in the butt at high volume) but with each extra direct out it gets worse. I normally have and 8 channnel 1.5 meter snake for the direct outs and separate leads for the master. these got right into the multi core. with power running here and there for powered side fill lights the td30 ect ect

This sounds like an effective insertion point for the ferrites might be a) the power cable of the mixer and/or b) the power cable of TD-30.

Just envision or follow your conductors to see the loop and the big area it encircles: starting at TD-30 Direct Out 1, run over to the mixer, jump to its power cable, follow the power cable to its power plug, follow conductors to the power plug of TD-30, run up TD-30's power cable and jump to Direct Out 1. That's the loop.

Humming signals are everywhere in the air, e.g. generated by the high power lights, or giant amps around. So any electromagnetic hum signal, running passing said loop like a radio signal, will induce a humming signal, which will be picked up by the most sensitive part, e.g. in TD-30 or in the mixer and brought to your ears. Now, that you have other Direct Outs connected too, you have many of those loops, say 8, which give an 8 times stronger picked up humming signal.

You may succeed in breaking these 8 loops simultaneously by ring- or plug-on ferrits attached to the mixers and/or TD-30's power cable: they increase the impedance, the resistance, for the humming signal along these loops, and effectively reduce it. (It should work with the DO's as well, but then you'll need many more ferrites ;-)